ETHYL BROMIDE 57 through a funnel, the stem of which is drawn out so as to pass through the narrow neck. The bottle is placed in a mixture of * snow or pounded ice and left a quarter to half an hour, until the contents have a temperature of o°. The meniscus is now adjusted until it coincides with the mark on the neck of the bottle. If more liquid has to be added, this may be done from a small pipette with capillary de- ^ livery tube ; if some of the liquid has to be I ,*' removed, a thin roll of filter paper may be \ f inserted which will absorb it. The bottle is then stoppered,dried on the outside, left in the . l|* balance case for a quarter of an hour, and J weighed. It is then emptied, cleaned, and ' ( | dried, and filled with distilled water previously i boiled. The water is cooled to o°, the meniscus <' V adjusted and the bottle weighed, the same IG 45' process being repeated as that just described. -* The following expression will give the specific gravity of the . ' liquid at o° compared with water at o° :— . jf Where iu± — weight of empty bottle, w.2 = „ bottle,and water at o°, 7e/3 = „ bottle and liquid at o°; or, if compared with water at 4°, the above number must be multiplied by the density at o° = 0*999873. A very delicate and useful piece of apparatus, which is readily made with the blow-pipe, is Perkins5 modification of Sprengel's pyknometer.1 It is especially adapted for small quan- tities of liquid and for the more volatile ones. The apparatus (Fig. 46) consists of a U~tuDe to hold from 2 to 10 c.c., drawn out at each end into a fine capillary. The one capillary limb, #, is bent outwards and is furnished with a small bulb ; the other, £, is bent at a right angle with the first. On the limb <z, between the bulb and the top of the U-tube a mark is etched. The 1 Trans. Chem. Soc. 1884, 45, 421.